Ignition composition



g- 19, 1952 c. P. SPAETH ET AL 2 IGNITION COMPOSITION Filed Dec. 1, 1948 INVENTORS CHARLES PHIL/P SPAETH 8: BiqHARES PIERCE ILL/AMS- A T TORNEY-S Patented Aug. 19, 1952 ,VUNI'ITED STATES PATENT, "OFFICE 1 2,607,672. A k I H "IGNITION COMPOSITION I I Charles Philip Spaeth, Woodbury, andCharles Pierce Williams, Pitman, N. J assignors toE. I-

, du Pont de Nemours & Company, Wilmington, V Del., a corporation of Delaware 1 Application December 1, 1948, Serial No. 62,878

1 This invention relates to compositions capable of ready ignition, and more particularly to such compositions for use as firing charges in electric blasting caps.

Blasting cap charges comprise generally a base charge of a high-strength detonating explosive, a flame sensitive primer charge superposed on the base charge, and a readily ignitible ignition charge capable of firing the primer charge by the flame generated. In the case of delay caps, an additional slow-burning composition is included, between the ignition and primer charges, of such predetermined rate of burning that the specified time interval elapses between the application of the firing current and the explosion of the primer charge.

Two desirable features of delay blasting caps are that (1) the delay composition be protected from moisture penetration even when used under wet conditions, and (2) no excessive pressure be allowed to develop in the cap shell as a result of the gaseous combustion products. Theattainment of .both desiderata simultaneously requires that a ventless shell be used and that relatively little or no gaseous products be formed before the rupture of the shell by the explosion of the main charges. While considerable progress has been made in attempts to accomplish the foregoing objectives by the use of ignition and delay compositions that produce substantially no, or relatively small amounts of, gas on combustion, further advances are desirable.

An object of the present invention is a novel and improved ignition composition. A further object is such a composition characterized by ready ignitibility and the production of relatively small amounts of gaseous combustion products. A still further object is such a composition excellently adapted for use in delay electric blasting caps. Further objects will be disclosed as the invention is described further hereinafter.

We have found that the foregoing objects are accomplished when we utilize as an ignition composition a blend in finely divided condition of metallic bismuth and an elemental material taken from the group consisting of sulfur, selenium and tellurium. We preferably include also in minor proportion an inorganic oxygen-supplying ingredient such as potassium chlorate.

A specific application and the functioning of the invention will be shown by reference to the attached drawing, which shows a cross-sectional view of a delay electric blasting cap including the proposed ignition composition. In the figure,

4 Claims.

i represents a metal capshell having a base charge 2 of a highvelocitydetonating explosive, e. g. tetryl. Above this is aprimer charge 3 of lead azide or other like primary detonating composition, while superposed thereon is a metal carrier 5, having a longitudinal central perforation. In this bore is contained the delay charge A, which may be of any desired composition having such characteristics that the rate of burning is of the desired, predetermined order and which produces substantially gasless combustion products. A suitable mixture, for example, comprises a balanced blend of selenium and barium peroxide. Above the delay carrier is positioned an ignition composition in accordance with this invention, and a desirableone is a 48-47-5 mixture of bismuth-selenium-potassium chlorate respectively. The cap shellis closed tightly at its upper end by a molded rubber plug 8, through which pass the insulated wires 1. These wires are free from insulation at their lower ends and extend beyond the inner surface of the rubber plug, their bared ends being connected by a small-diameter, highly resistant bridge wire 9, which is embedded in the mass of loose ignition mixture 6. At thetime of firing, the electric current passes through wires I and bridge wire 9, the latter becoming sufficiently heated to ignite the charge 6, which in turn efiects combustion of the delay powder 4. The detonating explosive charges thereby become exploded, after a predetermined time interval.

While an additional oxidizing agent, potassium chlorate, has been included in the composition in the drawing, the essential feature of the invention is an ignition composition comprising metallic bismuth and an elemental material taken from the group consisting of sulfur, selenium, and tellurium. For the purpose of ready ignitibility, these ingredients should be in finely divided condition and thoroughly blended, a suitable degree of fineness being such for example that both the bismuth and the selenium or other material will pass a ZOO-mesh screen. Various oxidizing agents may desirably be included in small proportion in the compositions, for example potassium permanganate, barium peroxide, potassium chlorate and the like. We find desirable proportions of ingredients to be 40 to 75% bismuth, to 25% selenium, and 0.5 to 5.0% potassium chlorate, when this latter is present. As examples of preferred compositions, we may cite 48-47-5, 61-36-3 and 63-33-4 mixtures respectively of bismuth, selenium and potassium chlorate. Small amounts of various diluents and the compositions disclosed maybe used as ignition compositions or burning chargesgener-all-y.

They may,.for example, be employed as delay compositions in blasting initiators.

It will be understood that, when the burning charges of this invention are used in blasting caps, various delay, primer and base charges may be present, such primer charges as mercury fulminate, fulminate-chlorate compositions, lead azide and the like, and base charges of tetryl, pentaerythritol tetranitrate, etc. Such supplementary charge compositions are not a part of our invention.

The burning compositions disclosed possess a number of advantages. In the first place, they produce combustion products that are substantially free from gases; hence the charges are highly suitable for use in delay caps, from this point of view. They are readily'ignitible even with relatively low firing currents, and are satisfactory with respect to impact sensitivity and thermal stability on storage for long periods of time. Delay electric blasting caps containing either 6 1-3-3 or 63*33-4 bismuthsclenium-potassium' chlorate'cha'rges, for example, performed satisfactorily after 6 months storage atboth normal temperature and 120 While the use of selenium has been stressed in the foregoing, sulfur and tellurium are likewise applicable, as each of these elements resembles oxygen inits ability to combine directly with bismuth. When selenium alone is present with bismuth in the proper proportions, bismuth selenide, BizSa, is considered to be the non gaseous reaction product. Relatively little heat results from the reaction of bismuth and selenium, and this fact is advantageous in 'many respects. In other cases, however, a slightly hotter or more readily ignitable composition is desired, and this result is obtained by inclusion in the mixture of a small amount of an oxidizing agent such as potassium chlorate, whereby oxidation of a portion ofthe bismuth to the oxide may occur. While the foregoing explains generally the reactions taking place, it will be understood that the invention is not limited by the explanation given and that Various alternative reactions may occur.

The invention has been adequately disclosed in the foregoing. It will be understood, however, that many variations in details of compositions and applications may be introduced without departure from the scope of the invention.

We intend to be limited, therefore, only by the following claims.

We claim:

1. An ignition composition comprising bismuth the proportion of 40 to 75% by weight, selenium in the proportion of between and 25% by weight and a minor percentage of an inorganic oxygen-supplying ingredient taken from the class consisting of potassium permanganate, barium peroxide, and potassium chlorate.

'2. The ignition composition of claim 1, in which the oxygen supplyin'g ingredient is barium peroxide.

3. The ignition composition of claim 1, in which the oxygen-supplying ingredient is potassium chlorate.

4. An ignition composition comprising between 40 and by weight of metallic bismuth, between 60 and 25% of selenium, and potassium chlorate in an amount between 0.5 and 5.0%.

CHARLES PHILLIP SPAETH. (DHARLE'S PIERCE WILLIAMS.

REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,095,302 Woodford Oct. 2, 1937 2,111,203 Mar. 15, 1938 2,168,030 Holmes Aug. 1, 1939 2,370,159 Hanley s Feb. 27, 1945 2,395,045 Gr'afi Feb. 19, 1946 2,450,892 Hale Oct. 12, 1948 2,478,918 Hale et a1. Aug. 16, 1949 OTHER. REFERENCES 

1. AN IGNITION COMPOSITION COMPRISING BISMUTH IN THE PROPORTION OF 40 TO 75% BY WEIGHT, SELENIUM IN THE PROPORTION OF BETWEEN 60 AND 25% BY WEIGHT AND A MINOR PERCENTAGE OF AN IN- 